Low temperature heat shrinkable film for labels

ABSTRACT

The present invention provides a low temperature heat shrinkable film for labeling comprising at least one layer of a thermoplastic resin, in whose correlation diagram showing the relation between the heat shrinkage percentage Y at 80° C. in one direction and the heat shrinkage time t (1≦t≦5), the gradient Y′ is in an area between the gradients satisfying Equations 1 and 2 and the heat shrinkage percentage Y is in an area between the heat shrinkage percentages satisfying Equations 3 and 4: 
     
       
           Y ′=−1.05 t   2 +12.05 t   (Equation 1) 
       
     
     
       
           Y ′=−0.30 t   2 +2.90 t   (Equation 2) 
       
     
     
       
           Y =−1.05 t   2 +12.05 t +40  (Equation 3) 
       
     
     
       
           Y =−0.30 t   2 +2.90 t +9  (Equation 4)

TECHNICAL FIELD

The present invention relates to heat shrinkable films for labeling,which are excellent in low temperature heat shrinking properties and UVabsorbing properties.

BACKGROUND ART

It is a common practice to apply heat shrinkable films (labels) bearingprinting on the internal surface to containers such as plasticcontainers for exhibiting product names, instructions for use and otherinformation, or for decorative purposes (Japanese Unexamined PatentPublications Nos. 114380/1997 and 272182/1997).

Recently, however, there is remarkable increase in the number of plasticcontainers having low heat resistance and those made of thin sheets soas to facilitate recycling and decrease pollution caused by wasteincineration. On the other hand, aseptic filling is becomingincreasingly popular as a technique for filling containers. If a heatshrinkable film (label) is applied to an aseptically filled plasticcontainer having low heat resistance or made of a thin sheet, therearises the problem that the container is markedly deformed when the film(label) is shrunk by the conventional wet heat at about 85 to 90° C.Further, some products need to be labeled at the lowest possibletemperature to maintain their quality.

Accordingly, there is a strong demand for heat shrinkable films forlabeling which show proper shrinking properties at low temperatures (70to 84° C.).

Also demanded are low temperature heat shrinkable films for labelingwhich have UV absorbing properties (UV screening properties) to protectproducts prone to deterioration, change in quality or discoloration byUV light (such as medicines, foods, refined sake and like drinks, andcosmetics).

An object of the present invention is to provide a low temperature heatshrinkable film for labeling showing proper shrinking properties at lowtemperatures (70 to 84° C.).

Another object of the invention is to provide a low temperature heatshrinkable film for labeling comprising a specific resin system.

A further object of the invention is to provide a low temperature heatshrinkable film for labeling having excellent UV absorbing properties.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a label applied to a containerhaving a fill point, wherein 1 indicates a container; 2, a fillingpoint; 3, a label before heat shrinkage; 4, a label after heatshrinkage; and 5, the main orientation direction of the film.

FIG. 2 is a diagram showing gradients Y′ satisfying Equations 1, 2, 5and 6, respectively. The gradient Y′ according to the invention is inthe area between the gradients of Equations 1 and 2, more preferably inthe area between the gradients of Equations 5 and 6.

FIG. 3 is a diagram showing heat shrinkage percentages Y satisfyingEquations 3, 4, 7 and 8, respectively. The heat shrinkage percentage Yaccording to the invention is in the area between the heat shrinkagepercentages of Equations 3 and 4, more preferably in the area betweenthe heat shrinkage percentages of Equations 7 and 8.

FIG. 4 is a correlation diagram showing the gradients Y′ satisfyingEquations 1, 2, 9, 10, 11 and 12, respectively.

FIG. 5 is a correlation diagram showing the heat shrinkage percentages Ysatisfying Equations 3, 4, 9, 10, 11 and 12, respectively.

FIG. 6 is a chart showing the results of spectrophotometricdetermination of the transmission of UV light (and a slight amount ofvisible light) through the film obtained in Example 1.

FIG. 7 is a chart showing the results of spectrophotometricdetermination of the transmission of UV light through the film obtainedby following the procedure of Example 1 with the exception of not usingthe UV absorber.

SUMMARY OF THE INVENTION

The present inventors did extensive research to achieve the aboveobjects and found that these objects can be accomplished by a heatshrinkable film comprising at least one layer of a thermoplastic resin,in whose correlation diagram showing the relation between the heatshrinkage percentage Y at 80° C. in one direction (orientationdirection) and the heat shrinkage time t (sec) (1≦t≦5), the gradient Y′is in the area (hereinafter referred to as “Area A”) between thegradients satisfying Equations 1 and Equation 2 and the heat shrinkagepercentage Y is in the area (hereinafter referred to as “Area B”)between the heat shrinkage percentages satisfying Equations 3 and 4.

Y′=−1.05t ²+12.05t  (Equation 1)

Y′=−0.30t ²+2.90t  (Equation 2)

Y=−1.05t ²+12.05t+40  (Equation 3)

Y=−0.30t ²+2.90t+9  (Equation 4)

The present invention provide a low temperature heat shrinkable film forlabeling comprising at least one layer of a thermoplastic resin, inwhose correlation diagram showing the relation between the heatshrinkage percentage Y at 80° C. and the heat shrinkage time t (1≦t≦5),the gradient Y′ is in Area A (see FIG. 2) and the heat shrinkagepercentage Y is in Area B (see FIG. 3).

The present invention also provides a film containing a thermoplasticpolyester resin.

The present invention further provides a film comprising an intermediatelayer (B) comprising at least one resin selected from the groupconsisting of polystyrene resins, high impact polystyrene resins andhigh impact graft polystyrene resins, and inner and outer layers (A) and(C) each comprising a resin system mainly comprising a styrene-butadieneblock copolymer, the layers being laminated in the order (A)/(B)/(C).

The present invention further provides the above film wherein the innerand outer layers (A) and (C) each contain a mixed resin system of 100parts by weight of a styrene-butadiene block copolymer having abutadiene content of 10 to 40 wt. % and 2 to 100 parts by weight of apolystyrene resin.

The present invention also provides the above film wherein theintermediate layer (B) further contains a UV absorber.

The present invention also provides the above film having a maximumlight transmission of 25% or less, preferably 20% or less, morepreferably 15% or less, in the wavelength range of 250 to 380 nm.

The heat shrinkable film for labeling according to the invention can bepreferably applied to containers amenable to labeling by heat shrinkageat low temperatures (70 to 84° C.). Examples of such containers includeplastic containers having low heat resistance or made of thin sheets(such as polystyrene containers, polyethylene containers and PETcontainers for aseptic filling) which are deformed at 85° C. or higher,and containers which are preferred to be labeled by heat shrinkage atlow temperatures (70 to 84° C.) in order to maintain the quality of thecontents.

When a tubular heat shrinkable film (label) is placed around a containerand heat shrunk, the shrinkage percentage with respect to shrinkage time(i.e., shrinkage rate) greatly affects the finish conditions of thelabel. Further, plastic containers having low heat resistance or made ofthin sheets need to be labeled at a low temperature within a shortperiod of time. That is, the temperature and time for shrinkage, andshrinkage percentage are factors that may combine to cause defects suchas insufficient shrinkage, pockmarks, wrinkles and tucking of the filmand deformation of the container. The heat shrinkable film describedabove does not produce such defects and can be tightly affixed to thecontainer by heat shrinkage.

In the correlation diagrams (FIGS. 2 and 3) showing the relation betweenthe heat shrinkage percentage Y and the heat shrinkage time t (1≦t≦5),if the gradient Y′ exceeds the gradient satisfying Equation 1, or if theheat shrinkage percentage Y exceeds the heat shrinkage percentagesatisfying Equation 3, the film shrinks too rapidly when heated and islikely to cause defects such as uneven shrinkage, pockmarks and tuckingof the films. On the other hand, if the gradient Y′ is less than thegradient satisfying Equation 2, or if the heat shrinkage percentage Y isless than the heat shrinkage percentage satisfying Equation 4, defectssuch as insufficient shrinkage or wrinkles of the film may occur,failing to produce a good finish.

The upper limit of the gradient Y′ that produces a good finish is thegradient satisfying Equation 1, preferably Equation 5, in FIG. 2. Thelower limit of the gradient Y′ is the gradient satisfying Equation 2,preferably Equation 6, in FIG. 2.

Further, the upper limit of the heat shrinkage percentage Y is the heatshrinkage percentage satisfying Equation 3, preferably Equation 7, inFIG. 3. The lower limit of the heat shrinkage percentage Y is the heatshrinkage percentage satisfying Equation 4, preferably Equation 8, inFIG. 4.

Y′=−1.05t ²+12.05t  (Equation 1)

Y′=−1.00t ²+11.00t  (Equation 5)

Y′=−0.30t ²+2.90t  (Equation 2)

Y′=−0.50t ²+4.50t  (Equation 6)

Y=−1.05t ²+12.05t+40  (Equation 3)

Y=−1.00t ²+11.00t+37  (Equation 7)

Y=−0.30t ²+2.90t+9  (Equation 4)

Y=−0.50t ²+4.50t+9  (Equation 8)

The low temperature heat shrinkable film for labeling according to theinvention can be prepared from a themoplastic resin, in particular apolystyrene resin. Preferred films include those comprising anintermediate layer (B) containing at least one resin selected from thegroup consisting of polystyrene resins, high impact polystyrene resinsand high impact graft polystyrene resins, and inner and outer layers (A)and (C) each containing a resin system mainly comprising astyrene-butadiene block copolymer, the layers being laminated in theorder (A)/(B)/(C).

The polystyrene resins usable in the invention include homopolymers andcopolymers of styrene, α-methyl styrene, p-methyl styrene and otherstyrene derivatives; copolymers of styrene or styrene derivatives andother monomers copolymerizable therewith, such as acrylic acid,methacrylic acid, their metal salts (e.g., Na, K, Li, Mg, Ca, Zn andFe), acrylic acid esters, methacrylic acid esters, other aliphaticunsaturated carboxylic acids, and their derivatives.

The high impact graft polystyrene resin is a styrene resin basicallycomprising a continuous phase of any of the above styrene resins andparticles of rubber-like polymer dispersed the continuous phase, therubber-like polymer having the styrene resin incorporated therein andgrafted to the rubber component such as polybutadiene.

The high impact polystyrene resin is a mixture of polystyrene and asynthetic rubber such as polybutadiene or polyisoprene, or a copolymerobtained by graft polymerization of styrene and a synthetic rubber suchas polybutadiene or polyisoprene.

The layers for forming the film can be laminated by any conventionalmethods such as dry lamination and extrusion lamination, among whichco-extrusion lamination is simple and thus preferable. Co-extrusionlamination can be performed using a T die to produce a flat film, orusing a die to prepare a tubular film which is then cut into a flatfilm.

The inner and outer layers (A) and (C) and the intermediate layer (B)may contain, within the range that does not adversely affect theirproperties, other resins such as polyethylenes (including copolymerscomprising ethylene as a main component and propylene, butene-1, vinylacetate or like monomer), polypropylenes (including copolymerscomprising propylene as a main component and ethylene, butene-1 or likemonomer) and other polyolefin resins, thermoplastic elastomers (e.g.,block copolymerization elastomers comprising polystyrene block andpolybutadiene block), rubbers and hydrocarbon resins. Further, eachlayer may contain any of various additives, such as fillers, heatstabilizers, antioxidants, antistatic agents, lubricants, nucleatingagents, flame retardants and coloring agents.

Thermoplastic resins usable in the invention include polyester resins,polystyrene resins, high impact polystyrene resins, high impact graftpolystyrene resins and like polystyrene resins, polyethylenes,polypropylenes and like polyolefins, and polyvinyl chloride resins.

The inner and outer layers (A) and (C) may be surface-treated to improveprintability. The surface treatment may be performed by any conventionalmethods, among which corona discharge treatment, plasma treatment andflame treatment are simple and thus preferable.

The thickness of the intermediate layer (B) accounts for 5 to 95%,preferably 40 to 95%, more preferably 65 to 85%, of the total thicknessof the film.

The inner layer (A) and outer layer (C) may be the same or different incomposition.

The film may contain, in addition to the layers (A)/(B)/(C), one or morelayers to form, for example, a structure (A)/(B)/(A)/(B)/(C). Further,the internal or external surface of at least one of layers (A) and (C)may be provided with a layer of a resin such as polyethylene (which maybe a copolymer such as an ethylene-vinyl acetate copolymer),polypropylene (which may be a copolymer such as a propylene-butene-1copolymer) or like polyolefin resin or polyester resin, optionally viaan adhesive layer.

It is more preferable that the inner and outer layers (A) and (C) eachcomprise a mixed resin system of the polystyrene resin and astyrene-butadiene block copolymer having a MI (melt index) of 0.5 to 10and a butadiene content of 10 to 40 wt. % (preferably 20 to 30 wt. %,more preferably 23 to 27 wt. %).

The styrene-butadiene block copolymer for use in the invention is acopolymer comprising styrene blocks and butadiene blocks. Examples ofsuch copolymers include S—B—S and (S—B)n-S, wherein S is a styreneblock, B is a butadiene block and n is an integer of 2 or more. Alsousable are those wherein part of residual double bonds have beenhydrogenated.

The mixing ratio of the polystyrene resin to the block copolymer is 2 to100 parts by weight, preferably 7 to 50 parts by weight, more preferably12 to 25 parts by weight of the polystyrene resin, to 100 parts byweight of the block copolymer.

The inner layer (A) and outer layer (C) may be different from each otherin MI, butadiene content, polystyrene resin content or thickness. It ispreferable, however, that the inner and outer layers are equivalent inthese values, from the viewpoint of prevention of curling of the film.

Further, terpolymers and tetrapolymers containing other component aswell as the styrene-butadiene block copolymer, can be used in thepresent invention. Examples of other components include acrylic acid,methacrylic acid and their metal salts (e.g., Na, K, Li, Mg, Ca, Zn andFe), acrylic acid esters, methacrylic acid esters, other aliphaticcarboxylic acids and their derivatives. When the terpolymer ortetrapolymer is used, the butadiene content and the amount of thepolystyrene resin to be added are preferably the same as in the casewhere the styrene-butadiene block copolymer is used.

The film comprising the layers (A)/(B)/(C) is rendered heat shrinkableby orientating it in the desired direction of heat shrinkability (and inthe direction perpendicular to said direction, where necessary).

As used herein, the heat shrinkage direction (one direction) of the heatshrinkage percentage Y is the orientation direction when the film ismonoaxially orientated. or the direction of a higher orientation ratiowhen the film is biaxially orientated simultaneously or sequentially.

An embodiment of the process for producing the laminate film of theinvention will be specifically described below. Using three extruders,resins for forming the inner layer (A), intermediate layer (B) and outerlayer (C), are respectively melted, and the molten resins are laminatedby fusing in one T die. The laminate film is extruded from the T die,taken off with a take-off roll, orientated with nip rolls in the machinedirection, orientated with a tenter in the transverse direction,annealed, cooled and wound up with a wind-up roll, to thereby obtain aheat shrinkable film. (The film may be orientated in only one of themachine and transverse directions.)

The heat shrinkable film of the invention is 10 to 150 μm thick, usually20 to 70 μm thick.

The heat shrinkage percentage (heat shrinkage rate) is determined bytypes and proportions of the resins constituting the film, filmthickness, extrusion temperature, draw ratio, take-off temperature,orientation ratio, orientation rate, orientation temperature, annealingconditions and cooling conditions, all of which are closely related withone another. By selecting suitable conditions, the low temperature heatshrinkable film of the invention can be obtained, in whose correlationdiagram showing the relation between the heat shrinkage percentage Y at80° C. in one direction and the heat shrinkage time t (1≦t≦5), thegradient Y′ is in Area A and the heat shrinkage percentage Y is in AreaB. Preferred conditions are described in the following Example 1.

In the film having the structure (A)/(B)/(C), the inner and outer layers(A) and (C) chiefly serve to impart suitable shrinking properties at lowtemperatures (70 to 84° C.) and improve impact resistance, and theintermediate layer (B) to improve stiffness and decrease the naturalshrinkage percentage (to 2% or less).

The natural shrinkage percentage of the film of the invention ispreferably 2% or less, more preferably 1.5% or less.

The layer (B) may contain a styrene-butadiene block copolymer, and thefilm may have a structure (B)/(A)/(B), instead of (A)/(B)/(C).

A UV absorber may be added for imparting UV absorbing properties to thefilm. Useful UV absorbers are not limited and include known UV absorberssuch as 2,2-hydroxy-5-methylphenylbenzotriazole,2,2-hydroxy-3-t-butyl-5-methylphenyl-5-chlorobenzotriazole,2,2-hydroxy-3′,5′-di-t-butylphenyl-5-chlorobenzotriazole and likebenzotriazole UV absorbers; 2-hydroxy-4-methylbenzophenone and likebenzophenone UV absorbers;2,4-di-t-butylphenyl-3,5-di-butyl-4-hydroxybenzoate and likehydroxybenzoate UV absorbers; and titanium oxide and like inorganic fineparticles. These UV absorbers may be used singly or in combination.Benzotriazole UV absorbers are particularly effective and thuspreferable.

UV absorbing properties required of the film vary according to theproduct to be labeled for sale or distribution, but generally, the filmhas a maximum light transmission of 25% or less, preferably 15% or less,in the wavelength range of 250 to 380 nm. The UV absorber is added in anamount that can achieve the above effect, i.e., usually in an amount of0.05 to 2 parts by weight per 100 parts by weight of the film.

The UV absorber can be added to at least one of the inner and outerlayers (A) and (C) and intermediate layers (B). It is more preferable toadd the UV absorber only to the intermediate layer (B), since, in thatcase, the inner and outer layers (A) and (C) serve as screen layers andprevent the UV absorber from diffusing during extrusion or orientationof the film, thus making it possible to impart sufficient properties byaddition of only a small amount of the UV absorber.

The low temperature heat shrinkable film thus obtained is provided withprinting on the surface of the inner layer, made into a tube having aprinted internal surface by center sealing, and cut in a proper lengthto give a label. The label is placed around a plastic container havinglow heat resistance or made of a thin sheet, and heat shrunk at a lowtemperature, whereby the contemplated results can be achieved.

When the label has UV absorbing properties, the label covers preferablythe whole surface of the container except for the minimum areas in theopening portion and bottom portion, so that the highest effect can beachieved.

The low temperature heat shrinkable film of the invention can be alsoprepared from a layer of a polystyrene resin. The polystyrene resin isnot limited, and the above resins for use in the layers (A), (B) and (C)can be preferably used.

The low temperature heat shrinkable film can be obtained, in whosecorrelation diagram showing the relation between the heat shrinkagepercentage Y at 80° C. in one direction and the heat shrinkage time t(1≦t≦5), the gradient Y′ is in Area A and the heat shrinkage percentageY is in Area B, by suitably selecting types and proportions of resins,film thickness, extrusion temperature, draw ratio, take-off temperature,preliminary heating conditions, orientation ratio, orientation rate,orientation temperature, annealing conditions and cooling conditions.

UV absorbing properties can be imparted to the film by adding anecessary amount of the above UV absorber.

The low temperature heat shrinkable film of the invention can be alsoprepared from a thermoplastic polyester resin. Preferred thermoplasticpolyester resins include those mainly comprising a copolymerizedpolyester resin. The acid components forming the copolymerized polyesterresins may be known acids, such as terephtharic acid, isophthalic acid,phthalic acid, 2,6-naphthalenedicarboxylic acid and like naphthalenedicarboxylic acids; diphenyl 4,4′-dicarboxylate and likedicarboxybiphenyls; 5-t-butylisophthalic acid and like substitutedphthalic acids; 2,2,6,6-tetramethylbiphenyl-4,4′-dicarboxylic acid andlike substituted dicarboxybiphenyls;1,1,3-trimethyl-3-phenylindene-4,5-dicarboxylic acid and itssubstitution products; 1,2-diphenoxyethane-4,4′-dicarboxylic acid, itssubstitution products and like aromatic dicarboxylic acids; oxalic acid,malonic acid, succinic acid, glutaric acid, adipic acid, azelaic acid,sebacic acid, pimelic acid, suberic acid, undecanoic acid,dodecanedicarboxylic acid, brasylic acid, tetradecanedicarboxylic acid,thapsinic acid, nonadecanedicarboxylic acid, docholinedicarboxylic acidand like aliphatic dicarboxylic acids, and their substitution products;and 4,4′-dicarboxycyclohexane and like alicyclic dicarboxylic acids andtheir substitution products. Useful diol components include known diols,such as ethylene glycol, triethylene glycol, propylene glycol,butanediol, 1,6-hexanediol, 1,10-decanediol, neopentyl glycol,2-methyl-2-ethyl-1,3-propanediol, 2-diethyl-1,3-propanediol,2-ethyl-2-n-butyl-1,3-propanediol and like aliphatic diols;1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol and like alicyclicdiols; ethylene oxide adducts of bisphenol compounds such as2,2-bis(4′-β-hydroxyethoxydiphenyl)propane andbis(4′-β-hydroxyethoxyphenyl)sulfone; xylylene glycol and like aromaticdiols; and diethylene glycol.

The copolymerized polyester resins may be used singly or in combination,or as mixed with a small amount of a polyethylene terephthalate resin,polybutylene terephthalate resin or the like.

The low temperature heat shrinkable film can be obtained, in whosecorrelation diagram showing the relation between the heat shrinkagepercentage Y at 80° C. in one direction and the heat shrinkage time t(1≦t≦5), the gradient Y′ is in Area A and the heat shrinkage percentageY is in Area B, by suitably selecting types and proportions of resins,film thickness, extrusion temperature, draw ratio, take-off temperature,preliminary heating conditions, orientation ratio, orientation rate,orientation temperature, annealing conditions and cooling conditions.Preferred conditions are, for example, those described in the followingExample 3.

The heat shrinkable film of the invention comprising the themoplasticpolyester resin not only is capable of forming a label with propershrinkage properties at low temperatures but also has excellent impactresistance, good stiffness and low natural shrinkage percentage of 2% orless, owing to the properties of the resin.

UV absorbing properties can be imparted to the film by adding anecessary amount of the above UV absorber.

The low temperature heat shrinkable film of the invention can be alsoprepared from a polyvinyl chloride resin. The polyvinyl chloride resinis not limited, but is preferably a composition comprising 100 parts byweight of a homogeneous polyvinyl chloride resin with a polymerizationdegree of 750 to 800, 6 to 6.5 parts by weight of a plasticizer (such asdioctyl adipate), 9 to 10 parts by weight of an impact modifier (ABSresin) and a small amount of a stabilizer.

The low temperature heat. shrinkable film can be obtained, in whosecorrelation diagram showing the relation between the heat shrinkagepercentage Y at 80° C. in one direction and the heat shrinkage time t(1≦t≦5), the gradient Y′ is in Area A and the heat shrinkage percentageY is in Area B, by suitably selecting types and proportions of resins,film thickness, extrusion temperature, draw ratio, take-off temperature,preliminary heating conditions, orientation ratio, orientation rate,orientation temperature, annealing conditions and cooling conditions.

UV absorbing properties can be imparted to the film by adding anecessary amount of the above UV absorber.

In the correlation diagram showing the relation. between the heatshrinkage percentage Y and the shrinkage time t according to theinvention, the heat shrinkage time t is equal to or less than 5, becausethe finish conditions of shrunk labels are determined in 5 seconds orless of heat shrinkage time. Accordingly, labeled containers may be inthe shrink tunnel for a period exceeding 5 seconds, on condition thatthe deformation of the container be within an acceptable range.Similarly, the film of the invention can be shrunk by heating at atemperature exceeding 84° C., depending on the type of the container tobe which the film is applied.

The heat shrinkable film of the invention is heat shrunk preferably at70 to 84° C. for about 4 to 5 seconds. The heat shrinkage percentage ofthe film of the invention is about 15 to 75%, preferably about 20 to65%.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Typical embodiments of the present invention are given below toillustrate the invention in further detail.

The following methods were employed for obtaining the correlationdiagram showing the relation between the heat shrinkage percentage Y at80° C. in one direction and the heat shrinkage time t (1≦t≦5), measuringthe property values, and evaluating the test results.

The correlation diagram showing the heat shrinkage percentage Y at 80°C. in one direction and the shrinkage time t (1≦t≦5) was obtained by thefollowing method.

First, 30 samples, each measuring 100 mm×100 mm, were cut out from theheat shrinkable film.

One of the samples was immersed in a water bath at 80° C. for 1 secondand immediately cooled with cold water. Then measured was the length L(mm) in the machine or transverse direction (the direction to becomeparallel to the circumferential direction of the container at the timeof application of the film, the direction being hereinafter referred toas “main orientation direction”). Subsequently, the heat shrinkagepercentage was found by subtracting L from 100. The same procedure wasrepeated using nine of the remaining samples to find the average heatshrinkage percentage of the 10 samples. The obtained value was used asthe heat shrinkage percentage Y when t was 1. The heat shrinkagepercentage Y when t was 3 and the heat shrinkage percentage Y when t was5 were found by similar procedures.

Then, the values of a, b and c were found by substituting the value of Ywhen t was 1, value of Y when t was 3, and value of Y when t was 5, forY in the equation Y=at²+bt+c, whereby the relational expression can beobtained.

The correlation diagram of the gradient Y′ and the shrinkage time t wasobtained by plotting Y−c(=Y′) along the ordinate axis and t along theabscissa axis, within the range 1≦t≦5. Further, the correlation diagramof the heat shrinkage percentage Y and the heat shrinkage time t wasobtained by plotting Y along the ordinate axis and t along the abscissaaxis.

FIG. 2 shows the area in which the gradient Y′ according to the presentinvention lies, the area being defined by Equations 1 and 2 andEquations 5 and 6. FIG. 4 shows the correlation diagram of Equations 1and 2, respectively.

FIG. 3 shows the area in which the heat shrinkage percentage Y accordingto the invention lies, the area being defined by Equations 3 and 4, andEquations 7 and 8. FIG. 5 shows the correlation diagram of Equations 3and 4, respectively.

The natural shrinkage percentage of the film was determined by allowingthe film at 40° C. for 7 days and measuring the shrinkage percentage inthe main orientation direction.

The maximum light transmission in the wavelength range of 250 to 380 nmwas determined using a spectrophotometer “U-3410” manufactured byHitachi, Ltd.

The finish conditions of the shrunk label were observed, and evaluatedas good when the label was smooth and had no defects, and as poor whenthe label had any defects.

The change in height of the filling point (unit: mm) was determinedusing a PET bottle having a cylindrical body, by subtracting thedistance between the fill point and the bottom before the heat shrinkageprocess, from said distance after the heat shrinkage process. Thegreater the determined value, the greater the degree of heat deformationof the PET bottle.

EXAMPLE 1

In each of two extruders was melted a resin system for the outer andinner layers (A) and (C) consisting of 100 parts by weight of astyrene-butadiene block copolymer having a structure (S—B)₂—S and abutadiene content of 25 wt.%, and 18 parts by weight of a styrenemonopolymer. In another extruder was melted a resin system for theintermediate layer (B) consisting of 100 parts by weight of a highimpact graft polystyrene resin (“Asahi Chemical Polystyrene SS-700”manufactured by Asahi Chemical Industry Co., Ltd.), 8 parts by weight ofan elastomer resin (“Toughprene 126” manufactured by Asahi ChemicalIndustry Co., Ltd.) and 0.3 parts by weight of2,2-hydroxy-3-t-butyl-5-methylphenyl-5-chlorobenzotriazole. The moltenresin systems were laminated by fusing in one T die at 195° C. so as togive a film consisting of layers (A)/(B)/(C) in this order, which wasthen extruded from the T die, and taken off at a draw ratio of 118% witha take-off roll at 25° C. The film was orientated 1.4 times in themachine direction using an orientation roll at 85° C. and an orientationrate of 365%/min, preliminarily heated at 115° C. for 6 seconds, andorientated 5 times in the transverse direction using a tenter at a firstzone temperature of 105° C., a second zone temperature of 93° C. and anorientation rate of 5330%/min. The orientated film was then annealed inthe vicinity of the exit of the tenter at 98° C. over a period of 2.5seconds while relaxing the film by 1% in the widthwise direction, andsubjected to primary cooling with air at 75° C. and then to secondarycooling with a cooling roll at 30° C.

In the obtained film, the inner and outer layers (A) and (C) were each 9μm thick. and the intermediate layer (B) 42 μm thick. The totalthickness of the film was 60 μm.

The film had a natural shrinkage percentage of 1%, and a maximum lighttransmission of 12% in the wavelength range of 250 to 380 nm. Theresults of spectrophotometric determination are shown in FIGS. 6 and 7.(FIG. 6 shows the determination results of the film obtained in Example1, and FIG. 7 shows, for reference, those of the film obtained byrepeating the procedure of Example 1 except that the UV absorber was notused.) The relation between the heat shrinkage percentage Y and heatshrinkage time t of the obtained film is expressed by the followingEquation 9. FIG. 5 shows the correlation diagram of Equation 9, and FIG.4 the correlation diagram of the gradient Y′. FIGS. 4 and 5 reveal thatEquation 9 is in both Areas A and B according to the invention.

Y′=−0.750t ²+9.00t +21.750  (Equation 9)

Subsequently, the surface of the layer (A) of the heat shrinkable filmwas provided with five-color photogravure using a photogravure printingmachine.

Then, using an organic solvent, the film was made into a tube having aninternal diameter of 71 mm by center sealing, so that the surface of thelayer (A) became the internal surface and the transverse direction ofthe film became parallel to the circumferential direction of thecontainer. The resulting tubular film was cut in a length of 64 mm toobtain a label.

EXAMPLE 2

A PET bottle for aseptic filling having a cylindrical body with anexternal diameter of 62.88 mm and a length of 170 mm and a fill point ata height of 172.8 mm from the bottom, was filled with water to the fillpoint, and sealed with a cap. The bottle was then covered with the labelobtained in Example 1, and passed through a wet heat shrink tunnel(length: 3 m, vapor pressure: 0.3 kg/cm2) for heat shrinking the labelat 80° C. for 5 seconds.

Table 1 shows the finish conditions of the shrunk label and change inheight of the fill point.

Comparative Example 1

A heat shrinkable film was prepared in the following manner, using aresin system for the inner and outer layers (A) and (C) consisting of100 parts by weight of a styrene-butadiene block copolymer having astructure (S—B)₂—S and a butadiene content of 20% and 50 parts by weightof a polystyrene resin, and a resin system for the intermediate layer(B) consisting of 100 parts by weight of a high impact graft polystyreneresin (“Asahi Chemical Polystyrene SS-700” manufactured by AsahiChemical Industry Co., Ltd.) and 10 parts by weight of a polystyreneresin. The resin systems were laminated using the same film formingapparatus as used in Example 1, extruded from the T die at 185° C. takenoff at a draw ratio of 130% with a take-off roll at 65° C.,preliminarily heated at 120° C. for 6 seconds, orientated 6 times in thetransverse direction using a tenter at a first zone temperature 110° C.,a second zone temperature of 100° C. and an orientation rate of4500%/min, annealed in the vicinity of the exit of the tenter at 105° C.over a period of 3 seconds while relaxing the film by 3% in thewidthwise direction, and subjected to primary cooling by air at 85° C.and then to secondary cooling with a cooling roll at 35° C.

In the obtained film, the inner and outer layers (A) and (B) were each 7μm thick and the intermediate layer (C) was 46 μm thick. The totalthickness of the film was 60 μm.

The relation between the heat shrinkage percentage Y and the heatshrinkage time t of the obtained film is expressed by the followingEquation 11. FIG. 5 shows the correlation diagram of Equation 11, andFIG. 4 the correlation diagram of the gradient Y′. FIGS. 4 and 5 revealthat Equation 11 is outside Areas A and B.

Y′=−0.250t ²+3.50t +4.750  (Equation 10)

The film was provided with printing and center sealing in the samemanner as in Example 1 and cut into the same length as in Example 1,giving a label. The label was heat shrunk at 80° C. for 5 seconds in thesame manner as in Example 2.

Table 1 shows the finish conditions of the shrunk label and the changein height of the fill point. It is apparent from Table 1 that the labelobtained in this example had poor finish conditions, owing to the factthat Equation 10 is outside Area B.

Comparative Example 2

The label obtained in Comparative Example 1 was heat shrunk at 88° C.for 5 seconds. The results are shown in Table 1. Table 1 reveals thatthe label had better finish conditions. but had a greater change inheight of the fill point, which indicated that the PET bottle wasdeformed by the high temperature heat shrinkage.

Comparative Example 3

A heat shrinkable film was prepared in the following manner, using aresin system for the inner and outer layers (A) and (C) consisting of100 parts by weight of the same styrene-butadiene block copolymer asused in Example 1 and 10 parts by weight of a styrene homopolymer, and ahigh impact polystyrene resin for forming the intermediate layer (B).The resin systems were laminated using the same film forming apparatusas used in Example 1, extruded from the T die at 195° C. and taken offat a draw ratio of 105% with a take-off roll at 35° C. The obtained filmwas orientated 6 times in the machine direction using a bench-scaleorientation apparatus at 90° C. and an orientation rate of 5300%/min.

In the obtained film, the inner and outer layers (A) and (C) were each 3μm thick and the intermediate layer (B) was 44 μm thick. The totalthickness of the film was 50 μm.

The relation between the heat shrinkage percentage Y and the heatshrinkage time t of the obtained film is expressed by the followingEquation 11. FIG. 5 shows the correlation diagram of Equation 11, andFIG. 4 the correlation diagram of the gradient Y′. FIGS. 4 and 5 revealthat Equation 11 is outside Areas A and B.

Y′=−1.125t ²+14.50t+33.625  (Equation 11)

The film was provided with center sealing so that the machine directionof the film became parallel to the circumferencial direction, and cutinto the same length as in Example 1, giving a label. The label was heatshrunk at 80° C. for 5 seconds in the same manner as in Example 2.

Table 1 shows the finish conditions of the shrunk label and the changein height of the fill point. It is apparent from Table 1 that the labelobtained in this example had poor finish conditions, owing to the factthat Equation 11 is outside Areas A and B.

EXAMPLE 3

In an extruder was melted a resin system consisting of 100 parts byweight of a copolymerized polyester resin containing terephthalic acid(77 mol %), isophthalic acid (13 mol %) and adipic acid (10 mol %) asdicarboxylic acid components and ethylene glycol (94 mol %) andneopentyl glycol (6 mol %) as diol components, 30 parts by weight of apolyester resin containing terephthalic acid as a dicarboxylic acidcomponent and butanediol as a diol component, 50 parts by weight of acopolymerized polyester resin containing terephthalic acid as adicarboxylic acid component and ethylene glycol (70 mol %) and1,4-cyclohexane dimethanol (30 mol %) as diol components, and 20 partsby weight of a polyethylene terephthalate resin. The molten resin wasextruded from a T die at 270° C., taken off with a take-off roll at 20°C. so that the film passed through the take-off roll had a birefringenceof 1.65 or less. The film was then orientated 1.3 times in the machinedirection with an orientation roll at 90° C. and an orientation rate of12000%/min, preliminarily heated at 85° C. for 5 seconds, and orientated5 times in the transverse direction using a tenter at a first zonetemperature of 95° C., a second zone temperature of 90° C. and anorientation rate of 5000%/min. The orientated film was then annealed inthe vicinity of the exit of the tenter to 80 to 60° C. over a period of5 seconds while relaxing the film by 1.5% in the widthwise direction,and cooled with a cooling roll at 25° C., giving a 50 μm thick heatshrinkable film.

The film had a natural shrinkage percentage of 1%. The relation betweenthe heat shrinkage percentage Y and heat shrinkage time t of theobtained film is expressed by the following Equation 12. FIG. 5 showsthe correlation diagram of Equation 12, and FIG. 4 the correlationdiagram of the gradient Y′. FIGS. 4 and 5 reveal that Equation 12 is inAreas A and B according to the invention.

Y′=−0.625t ²+6.50t+17.125  (Equation 12)

The heat shrinkable film was provided with printing and center sealingin the same manner as in Example 1, and cut in the same length as inExample 1 to give a label. The label was heat shrunk at 80° C. for 5seconds in the same manner as in Example 2.

Table 1 shows the finish conditions of the shrunk label and the changein height of the fill point.

TABLE 1 Change in height of Finish conditions fill point (mm) Ex. 2 Good<0.1 Comp. Ex. 1 Poor — (insufficient shrinkage occurrence of wrinkles)Comp. Ex. 2 Good   2.5 Comp. Ex. 3 Poor — (occurrence of pockmarks andtucking) Ex. 3 Good <0.1

The present invention is carried out in the mode as described above, andhas the following advantages.

Labels can be obtained which show proper shrinking properties at lowtemperatures (70 to 84° C.) and which are advantageous to maintain thequality of products, when the heat shrinkable film is a film comprisingat least one layer of a thermoplastic resin, in whose correlationdiagram showing the relation between the heat shrinkage percentage Y at80° C. in one direction and the heat shrinkage time t (1≦t≦5), thegradient Y′ is in the area between the gradients satisfying Equations 1and 2 and the heat shrinkage percentage Y is in the area between theheat shrinkage percentages satisfying Equations 3 and 4.

When the heat shrinkable film for labeling comprises an intermediatelayer (B) containing at least one resin selected from the groupconsisting of polystyrene resins, high impact polystyrene resins andhigh impact graft polystyrene resins, and inner and outer layers (A) and(C) comprising a specific mixed resin system of specific proportions ofa styrene-butadiene block copolymer and a polystyrene resin, the layersbeing laminated in the order (A)/(B)/(C), the obtained label not onlyshows proper shrinking properties at low temperatures (70 to 84° C.) butalso has excellent impact resistance, good stiffness and a small naturalshrinkage percentage.

When the heat shrinkage film for labeling comprises a thermoplasticpolyester resin, the obtained label not only shows proper shrinkingproperties at low temperatures (70 to 84° C.) but also has excellentimpact resistance, good stiffness and a small natural shrinkagepercentage.

When a UV absorber is added to obtain a film having a maximum lighttransmission of 25% or less in the wavelength range of 250 to 380 nm,products labeled with the film can be protected from deterioration,change in quality and discoloration caused by UV light.

If the UV absorber is added only to the intermediate layer (B) in themulti-layer polystyrene film, sufficient UV absorbing properties can beachieved by addition of only a small amount of the UV absorber.

What is claimed is:
 1. A heat shrinkable film for labeling comprising atleast one layer of a thermoplastic resin, in whose correlation diagramshowing the relation between the heat shrinkage percentage Y at 80° C.in one direction and the heat shrinkage time t (1≦t≦5), the gradient Y′is in the area between the gradients satisfying Equations 1 and 2 andthe heat shrinkage percentage Y is in the area between the heatshrinkage percentages satisfying Equations 3 and 4: Y′=−1.05t²+12.05t  (Equation 1) Y′=−0.30t ²+2.90t  (Equation 2) Y=−1.05t²+12.05t+40  (Equation 3)  Y=−0.30t ²+2.90t+9  (Equation 4).
 2. A heatshrinkable film according to claim 1, which comprises a thermoplasticpolyester resin.
 3. A heat shrinkable film according to claim 1, whichcomprises an intermediate layer (B) including at least one resinselected from the group consisting of polystyrene resins, high impactpolystyrene resins and high impact graft polystyrene resins, and innerand outer layers (A) and (C) each comprising a resin system mainlycomprising a styrene-butadiene block copolymer, the layers beinglaminated in the order (A)/(B)/(C).
 4. A heat shrinkable film accordingto claim 3, wherein the inner and outer layers (A) and (C) each comprisea mixed resin system of 100 parts by weight of a styrene-butadiene blockcopolymer having a butadiene content of 10 to 40 wt. % and 2 to 100parts by weight of a polystyrene resin.
 5. A heat shrinkable filmaccording to claim 3 or 4, wherein the intermediate layer (B) furthercomprises a UV absorber.
 6. A heat shrinkable film according to any oneof claims 1, 2, 3, or 4, wherein the film has a maximum lighttransmission of 25% or less in the wavelength range of 250 to 380 nm. 7.A heat shrinkable film according to claim 5, wherein the film has amaximum light transmission of 25% or less in the wavelength range of 250to 380 nm.
 8. A method for affixing a heat shrinkable film, comprising:applying a film according to any one of claims 1, 2, 3, or 4 to acontainer amenable to labeling by heat shrinkage at 70 to 84° C., andheat shrinking the film at a temperature of 70 to 84° C.
 9. A method foraffixing a heat shrinkable film, comprising: applying a film accordingto claim 5 to a container amenable to labeling by heat shrinkage at 70to 84° C., and heat shrinking the film at a temperature of 70 to 84° C.10. A method for affixing a heat shrinkable film, comprising: applying afilm according to claim 6 to a container amenable to labeling by heatshrinkage at 70 to 84° C., and heat shrinking the film at a temperatureof 70 to 84° C.
 11. A method for affixing a heat shrinkable film,comprising: applying a film according to claim 7 to a container amenableto labeling by heat shrinkage at 70 to 84° C., and heat shrinking thefilm at a temperature of 70 to 84° C.
 12. A packaged article obtainableby affixing a film according to any one of claims 1, 2, 3, or 4 to acontainer by heat shrinkage.
 13. A packaged article obtainable byaffixing a film according to claim 5 to a container by heat shrinkage.14. A packaged article obtainable by affixing a film according to claim6 to a container by heat shrinkage.
 15. A packaged article obtainable byaffixing a film according to claim 7 to a container by heat shrinkage.